1. Field of the Invention
The present invention relates to a ski base, or sole, namely, the bottom part of the ski in contact with the snow and upon which the ski and the skier are supported.
The invention especially relates to an improved snow ski sole having excellent capability of absorbing waxes and durably retaining such waxes.
2. Description of the Prior Art
Ski soles generally are in the form of a sheet or a film having a thickness in the range 0.5 to 2 mm. They are made of polyolefinic plastic material and are preferably based on high density polyethylene (HDPE), which may optionally be of high molecular weight (number average molecular weight in the range of 150,000 to 450,000) which can be measured by gel permeation chromatography.
Soles of this type are produced by conventional extrusion techniques. Nonetheless, their properties of impact resistance, dye affinity and the capability of absorbing waxes (fat-like substances of the paraffinic type) are not very satisfactory, or they are even inadequate for the specific requirements of a ski sole.
Attempts have been made to improve the specific properties and qualities of the polyethylenes used for ski soles by modifying their structure, either by incorporating additives or by treatment with an agent promoting the porosity of HDPE.
Thus, U.S. Pat. No. 3,075,948 describes grafting of a polyolefin (and particularly a polyethylene) with a silane.
In the French Patent published under No. 2,478,877, it was proposed to modify the sliding surface by incorporating a substance which is soluble in non-aqueous liquids into the HDPE before extrusion, then converting it into sheet or film.
Very high molecular weight HDPE (number average molecular weight in the range of 300,000 to 8,000,000) is also used for making ski soles designed for world class competition. These soles are produced by sintering, a much more difficult technique than extrusion.
In Austrian Patent No. 332,273, a process is described for producing a ski sole made from sintered HDPE.